Sonar data compression

ABSTRACT

A survey system including a multibeam echo sounder and a beam selector for selecting beams with the largest amplitudes.

INCORPORATION BY REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/812,286 filed Mar. 7, 2020 which is a continuation of U.S. patentapplication Ser. No. 15/581,468 filed Apr. 28, 2017 which is acontinuation in part of U.S. patent application Ser. No. 15/476,137filed Mar. 31, 2017, now U.S. Pat. No. 10,132,924, which claims thebenefit of U.S. Prov. Pat. App. No. 62/329,631 filed Apr. 29, 2016 bothof which are included herein in their entireties and for all purposes.This application incorporates by reference, in their entireties and forall purposes, the disclosures of U.S. Pat. No. 3,144,631 concerningMills Cross sonar, U.S. Pat. No. 5,483,499 concerning Doppler frequencyestimation, U.S. Pat. No. 7,092,440 concerning spread spectrumcommunications techniques, U.S. Pat. No. 8,305,841 concerning sonar usedfor mapping seafloor topography, and U.S. Pat. No. 9,244,168 concerningfrequency burst sonar.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to underwater acoustical systems, methodsfor using underwater acoustical systems, and methods for processing andusing the data they produce.

Discussion of the Related Art

A month after the Titanic struck an iceberg in 1912, Englishmeteorologist Lewis Richardson filed a patent at the British PatentOffice for an underwater ranging device. Modern day successors toRichardson's invention are often referred to as SONAR (sound navigationand ranging) devices. Among these devices are ones using transducerarrays to project sound or pressure waves through a liquid medium andtransducer arrays to receive corresponding echoes from features thatscatter and/or reflect impinging waves.

Information about these features and their environment can be derivedfrom the echoes. For example, bathymetric surveys provide informationabout the depth of scattering centers, water column surveys provideinformation about scattering centers in the water column, and seafloorcharacterization surveys provide information about scattering centers atthe seafloor surface and below the seafloor surface.

SUMMARY OF THE INVENTION

The present invention provides a survey system.

In an embodiment, a sonar data compression system including a multibeamecho sounder for installation on a water going vehicle, the sonar datacompression system comprising: an acoustic transceiver for use with oneor more transducers in a single projector array and plural transducersin a single hydrophone array; the projector array arranged with respectto the hydrophone array to form a Mills Cross; a transceiver forsynthesizing a transmitter message, the message exciting a projectorarray such that a swath beneath the vehicle is ensonified; Q beamsformed by the hydrophone array, the Q beams sampled 1, 2, 3 . . . stimes during a time that echoes from the message reach the hydrophones;and, for each of the times that the beams are sampled, the beam with thelargest magnitude ß_(x1) is identified as a characterizing beam; whereinthe data associated with the characterizing beams are used as acompressed characterization of the ensonified region. And in anembodiment, the sonar data compression system wherein: for each of thetimes that the beams are sampled, the beam with the second largestmagnitude ß_(x2) is identified as a characterizing beam. And in anembodiment, the sonar data compression system wherein: for each of thetimes that the beams are sampled, the beams with the largest Nmagnitudes ß_(x1) . . . ß_(xN) are identified as characterizing beamswhere N<Q. And in an embodiment, the sonar data compression systemwherein: the hydrophone array forms Q beams, u<Q beams defines asubsector, and from the subsector N largest beam magnitudes areidentified. And in an embodiment, the sonar data compression systemwherein: the hydrophone array forms Q beams, two subsectors are definedfrom the Q beams, and from each subsector N largest beam magnitudes areidentified. And in an embodiment, the sonar data compression systemwherein: the hydrophone array forms Q beams, three subsectors aredefined from the Q beams and from each subsector N largest beammagnitudes are identified. And in an embodiment, the sonar datacompression system wherein: the hydrophone array forms Q beams, S<Qsubsectors are defined from the Q beams, and from each subsector Nlargest beam magnitudes are identified.

In an embodiment a sonar data compression system including a multibeamecho sounder for installation on a water going vehicle, the sonar datacompression system comprising: an acoustic transceiver for use with oneor more transducers in a single projector array and plural transducersin a single hydrophone array; the projector array arranged with respectto the hydrophone array to form a Mills Cross; a transceiver forsynthesizing a transmitter message, the message exciting a projectorarray such that a swath beneath the vehicle is ensonified; Q beamsformed by the hydrophone array, the Q beams range gated at minimum andmaximum altitudes and sampled 1, 2, 3 . . . s times during a time thatechoes originating within the altitude limits reach the hydrophones;and, for each of the times that the beams are sampled, the beam with thelargest magnitude ß_(x1) is identified as a characterizing beam; whereinthe data associated with the characterizing beams are used as acompressed characterization of the ensonified region. And in anembodiment, the sonar data compression system wherein: the transceiversynthesizes n signals, for each of the n signals the output of arespective beamformer is sampled s times during a time that echoes fromthe message reach the hydrophones, and for each of the times that thebeams are sampled, the beam with the largest magnitude ß_(x1) isidentified as a characterizing beam, wherein the data associated withthe characterizing beams are used as a compressed characterization ofthe ensonified region.

In an embodiment a sonar data compression system including a multibeamecho sounder for installation on a water going vehicle, the sonar datacompression system comprising: an acoustic transceiver for use with oneor more transducers in a single projector array and plural transducersin a single hydrophone array; the projector array arranged with respectto the hydrophone array to form a Mills Cross; a transceiver forsynthesizing a transmitter message including plural different signalsSS1 . . . SSn; the transmitter message exciting a projector array suchthat a swath beneath the vehicle is ensonified; for each of n signals, abeamformer and a processor; for each of n beamformer outputs, theprocessors sample respective beams 1, 2, 3 . . . s times during a timethat echoes from the message reach the hydrophones; and, for each of thetimes that the beams are sampled, the beam with the largest magnitudeß_(x1) is identified as a characterizing beam; wherein the dataassociated with the characterizing beams are used as a compressedcharacterization of the ensonified region. And in an embodiment, thesonar data compression system wherein: for each of the sample times thatthe largest magnitude ß_(x1) and its associated beam angle α areidentified, the magnitude of beam data at the same beam angle and sampletime for all other beamformer outputs are identified providing afrequency dependent comparison of returns from the same scatterers atthe same time.

In an embodiment a sonar data compression system including a multibeamecho sounder for installation on a water going vehicle, the sonar datacompression system comprising: an acoustic transceiver for use with oneor more transducers in a single projector array and plural transducersin a single hydrophone array; the projector array arranged with respectto the hydrophone array to form a Mills Cross; a transceiver forsynthesizing a transmitter message, the message exciting a projectorarray such that a swath beneath the vehicle is ensonified; Q beamsformed by the hydrophone array, the Q beams sampled 1, 2, 3 . . . stimes during a time that echoes from the message reach the hydrophones;for each of the times that the Q beams are sampled, the beams with thelargest N<Q magnitudes ß_(x,N) are identified as characterizing beamsassociated with angle α_(x,N); for each of the times that the beams aresampled, a split array phase difference technique is applied where eachsub array is steered in direction α_(x,N); and, where the output of thetechnique provides an improved estimate of echo arrival angle relativeto the array face; wherein the magnitude from the characterizing beamsand the improved angle estimates are used as a compressedcharacterization of the ensonified region. And in an embodiment, thesonar data compression system wherein: the Q beams formed by thehydrophone array are range gated at minimum and maximum altitudes andsampled 1, 2, 3 . . . s times during a time that echoes originatingwithin the altitude limits reach the hydrophones. And in an embodiment,the sonar data compression system wherein: two subsectors are definedfrom the Q beams and from each subsector N<u largest beam magnitudes areidentified. And in an embodiment, the sonar data compression systemwherein: for each of n signals, a beamformer and a processor are used;and, for each of n beamformer outputs, the processors sample respectivebeams 1, 2, 3 . . . s times during a time that echoes from the messagereach the hydrophones.

In an embodiment a sonar data compression system including a multibeamecho sounder for installation on a stationary platform, the sonar datacompression system comprising: an acoustic transceiver for use with oneor more transducers in a single projector array and plural transducersin a single hydrophone array; the projector array arranged with respectto the hydrophone array to form a Mills Cross; a transceiver forsynthesizing a transmitter message, the message exciting a projectorarray such that a swath is ensonified; Q beams formed by the hydrophonearray, the Q beams sampled 1, 2, 3 . . . s times during a time thatechoes from the message reach the hydrophones; and, for each of thetimes that the beams are sampled, the beam with the largest magnitudeß_(x1) is identified as a characterizing beam; wherein the dataassociated with the characterizing beams are used as a compressedcharacterization of the ensonified region. And in an embodiment, thesonar data compression system wherein: for each of the times that the Qbeams are sampled, the beams with the largest N<Q magnitudes ß_(x,N) areidentified as characterizing beams associated with angle α_(x,N); foreach of the times that the beams are sampled, a split array phasedifference technique is applied where each sub array is steered indirection α_(x,N); and, where the output of the technique provides animproved estimate of echo arrival angle relative to the array face;wherein the magnitude from the characterizing beams and the improvedangle estimates are used as a compressed characterization of theensonified region.

As indicated herein, a variation of the method allows for extremelyprecise measurement of the angle to the echo, not constrained to thenominal beam directions of the beamformer. With such fine resolution inboth angle and time, locations of the most important scatterers can bederived precisely regardless of how they may be distributed in the watercolumn or sea floor. Variations of the method allow one or more peakmagnitudes to be identified from one or more subsets of beams from allor a subset of samples, thus giving flexibility in the amount ofinformation returned with each ping and the effective data compressionratio. Furthermore, the method can be applied to multiple messagecomponents per message cycle, each with a different center frequency,provided the multibeam echo sounder system supports the use of aplurality of non-overlapping frequency bands having respective centerfrequencies and bandwidths. This feature allows the collection ofsimultaneous frequency-dependent information from a set of scatteringcenters.

Notably, the sonar data compression system is not limited to use on awater going vehicle or any vehicle for that matter. For example, thesonar data compression system may be stationary for monitoring activityin a particular zone or area. For example, a stationary mounted MBESthat provides sonar data compression for use in a diver detectionsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanyingfigures. These figures, incorporated herein and forming part of thespecification, illustrate embodiments of the invention and, togetherwith the description, further serve to explain its principles enabling aperson skilled in the relevant art to make and use the invention.

FIG. 1A shows a survey system including a multibeam echo sounder systemof the present invention.

FIGS. 1B-G show embodiments of at least portions of the multibeam echosounder system of FIG. 1A.

FIG. 1H shows a legend of selected symbols.

FIG. 2 shows a message cycle used by the survey system of FIG. 1A.

FIGS. 3A-C show ensonification of a fan using the survey system of FIG.1A.

FIGS. 3D-E show sonar data compression after ensonification of a fanusing the survey system of FIG. 1A.

FIGS. 4A-I show sonar data compression after ensonification of one ormore partial sectors using the survey system of FIG. 1A.

FIGS. 5A-C show sonar data compression focused on the waterbody bottomand water column using the system of FIG. 1A.

FIGS. 6A-H show sonar data compression with multispectral returns usingthe survey system of FIG. 1A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The disclosure provided in the following pages describes examples ofsome embodiments of the invention. The designs, figures, and descriptionare non-limiting examples of the embodiments they disclose. For example,other embodiments of the disclosed device and/or method may or may notinclude the features described herein. Moreover, described features,advantages or benefits may apply to only certain embodiments of theinvention and should not be used to limit the disclosed invention.

As used herein, the term “coupled” includes direct and indirectconnections. Moreover, where first and second devices are coupled,intervening devices including active devices may be locatedtherebetween.

Multibeam Echo Sounder

FIGS. 1A-E show a survey system including a multibeam echo soundersystem and describe exemplary multibeam echo sounder embodiments. FIG.1H shows a legend 100H of selected symbols appearing on FIGS. 1C-G.

FIG. 1A shows a survey system in accordance with an embodiment of thepresent invention 100A. The survey system includes an echo soundersystem such as a multibeam echo sounder system 102 which may be mountedon a surface vehicle or vessel, on a waterbody bottom, on a remotelyoperated vehicle, on an autonomous underwater vehicle, or the like. Asis further described below, echo sounder and/or survey system outputs114 may be contemporaneous with echo sounder processing of hydrophonedata as in some embodiments for bathymetry or non-contemporaneous withprocessing of hydrophone data as in some embodiments for waterbodybottom classification.

Data acquired by multibeam echo sounder systems 104 include data fromecho sounder listening devices such as hydrophones (e.g., transducers)that receive echoes which are related to the acoustic/pressure wavesemanating from the echo sounder projectors but have returned by virtueof an interaction with inhomogeneities of many kinds. The interactionsmay take the form of reflection or scattering. The inhomogeneities, alsoknown as reflectors and scattering centers, represent discontinuities inthe physical properties of the medium. Exemplary scattering centers maybe found in one or more of i) an ensonified volume of the waterbody suchas a water column, ii) upon the ensonified surface of the bottom, oriii) within the ensonified volume of the sub-bottom.

Scattering centers of a biological nature may be present in the watercolumn, as they are a part of the marine life. Scattering centers of anonbiological nature may be present in the water column in the form ofbubbles, dust and sand particles, thermal microstructure, and turbulenceof natural or human origin, such as ships' wakes. Scattering centers onthe surface of the bottom may be due to the mechanical roughness of thebottom, such as ripples, or be due to the inherent size, shape andphysical arrangement of the bottom constituents, such as mud, sand,shell fragments, cobbles and boulders, or due to both factors.Scattering centers in the sub-bottom may be due to bioturbation of thesediments, layering of different sediment materials within the bottom orburied manmade structures such as pipelines.

Data processing within the echo sounder system may includecontemporaneous processing of hydrophone data 106, for example to obtainDoppler velocity data, bathymetric data, and/or backscatter data. Dataprocessing may also include non-contemporaneous processing of multibeamecho sounder system data 108, for example to characterize bottomconditions or the water column.

Data processing may include utilization of complementary or other data.For example, contemporaneous processing of hydrophone data 106 mayutilize contemporaneous 110 and/or non-contemporaneous 112 data such ascontemporaneously collected geographic positioning system (“GPS”) data,sound speed measurements, attitude, and navigational information. Forexample, non-contemporaneous processing of echo sounder system data mayutilize contemporaneous 110 and/or non-contemporaneous 112 data such asnon-contemporaneously collected waterbody bottom composition data andtidal records.

FIG. 1B shows portions of an exemplary multibeam echo sounder system(“MBES”) 100B. The echo sounder system includes a transducer section 120and an acoustic transceiver 122. The echo sounder system may include atransceiver interface such as an interface module 124 and/or aworkstation computer 126 for one or more of data processing, datastorage, and interfacing man and machine. Exemplary transducers, shownhere in a Mills Cross arrangement 120, include a transmitter orprojector array 130 and a receiver or hydrophone array 140. Projectorsin the projector array may be spaced along a line that is parallel witha keel line or track of a vehicle or vessel to which they are mountedwhich may be referred to as an along track arrangement. In someembodiments, a receiver of the transceiver 122 has an operatingfrequency range corresponding to that of the projectors and/or thehydrophones.

During echo sounder operation, sound or pressure waves emanating fromthe projector array travel within a body of water and possibly withinthe bottom beneath the body of water and in doing so may undergointeractions, such as reflections or scattering, which disturb thepropagation trajectory of the pressure waves. Some of the reflections orechoes are “heard” by the hydrophone array. See for example thedisclosure of Et al, U.S. Pat. No. 3,144,631, which is included hereinby reference, in its entirety and for all purposes.

The acoustic transceiver 122 includes a transmitter section 150 and areceiver section 170. The acoustic transceiver may be configured totransmit to one or more projector arrays 130 and to receive from one ormore hydrophone arrays 140. Unless otherwise noted, the term transceiverdoes not require common packaging and/or encapsulation of thetransmitter and receiver.

In various embodiments, a projector array may be a single projectorarray regardless of the geometry, arrangement, or quantity of devicesemployed. For example, where a plurality of projectors forms a pluralityof spatially distinct projector groups, the plural projectors are asingle projector array if they are operated to ensonify the entirety ofa swath on a single ping, for example a swath of waterbody bottom or aswath of water column. In various embodiments: i) a single projectorarray may ensonify the entirety of a swath on a single ping; ii) aplurality of projector arrays may ensonify the entirety of a swath on asingle ping; iii) a plurality of projector arrays ensonify multipleswaths on a single ping; and, iv) a plurality of projector arraysensonify one or more swaths on multiple pings.

The echo sounder may further include a means such as an interface module124 for interconnection with the transceiver 122. This interface modulemay provide, among other things, a power supply for the transceiver,communications with the transceiver, communications with the workstationcomputer 126, and communications with other sources of data such as asource of contemporaneous GPS data.

The workstation computer 126 may provide for one or more of dataprocessing such as data processing for visualization of survey results,for data storage such as storage of current profiling data, bathymetrydata, sound speed data, and backscatter data, for user inputs, and fordisplay of any of inputs, system status, and survey results.

FIG. 1C shows portions of an exemplary multibeam echo sounder system(“MBES”) 100C. The echo sounder system includes a transducer section120, a transmitter section 150, and a receiver section 170. Someembodiments include a sensor interface section 190 and/or a managementsection 192. And in some embodiments it is the management block thatsignals and/or provides instructions to the signal generators 158.

The transducer section includes transducers for transmitting acousticmessages and transducers for receiving acoustic messages. For example, atransducer section may include an array of projectors 130 and an arrayof hydrophones 140.

Projectors in the projector array 130 may include piezoelectric elementssuch as ceramic elements. Element geometries may include circular andnon-circular geometries such as rectangular geometries. Some projectorshave an operating frequency range of about 10 kHz to 100 kHz, of about50 kHz to 550 kHz, or about 100 to 1000 kHz.

Hydrophones in the hydrophone array 140 may include piezoelectricelements such as ceramic elements. Element geometries may includecircular and non-circular geometries such as rectangular geometries.Some hydrophones have an operating frequency range of about 10 kHz to100 kHz, of about 50 kHz to 550 kHz, or about 100 to 1000 kHz.

During operation of the projector array 130 and hydrophone array 140,the transmitter section excites the projector array, an outgoing message137 emanates from the projector array, travels in a liquid medium to areflector or scattering center 138, is reflected or scattered, afterwhich a return or incoming message 139 travels to the hydrophone array140 for processing by the receiver 170. Notably, the acoustic/pressurewave input 136 received at the hydrophone array 140 may include aDoppler shifted or otherwise modified version of the transmitted message137 along with spurious signal and/or noise content.

The transmit section 150 may include a signal generator block 158, atransmit beamformer block 156, a summation block 154, and a poweramplifier block 152. The transmit section provides for generation of orfor otherwise obtaining one or more signals or message components 158that will be used to compose a message 137. Notably, a message may becomposed of multiple signals or not. Where a message is composed ofmultiple signals, the message may contain i) signals in parallel(superposed), ii) signals that are serialized (concatenated), or iii)may be a combination of parallel and serial signals.

The transmit beamformer block 156 receives the signal(s) from the signalgenerator block 158 where beamforming for each signal takes place. Thebeam(s) are combined in the summation block 154 to construct a parallel,serial, or combination message M. In the power amplifier block 152, thetime series voltages of the message are amplified in order to excite ordrive the transducers in the projector array 130. In an embodiment, eachtransducer is driven by a respective amplifier.

The receive section 170 includes multiple hydrophone signal processingpipelines. In an embodiment the receive section includes a hardwarepipelines block/analog signal processing block 172, a software pipelinesblock/digital signal processing block 174, a receive beamformer block176, and a processor block 178. The receive section provides forisolating and processing the message 137 from the input 136 received atthe hydrophone array 140. For example, some embodiments process echoesto determine Doppler velocities and/or depths as a function of, amongother things, round trip travel times.

In the hardware pipeline block 172, plural hydrophone array transducersof the hydrophone array 140 provide inputs to plural hardware pipelinesthat perform signal conditioning and analog-to-digital conversion. Insome embodiments, the analog-to-digital conversion is configured foroversampling where the converter Fin (highest input frequency) is lessthan Fs/2 (one half of the converter sampling frequency). In anembodiment, a transceiver 122 operates with a maximum frequency of about800 kHz. In an embodiment the transceiver utilizes analog-to-digitalconverters with sampling rates in a range of about 5 to 32 MHz. In anembodiment the transceiver utilizes analog-to-digital converters withsampling rates of about 5 MHz or about 32 MHz.

In the software pipeline block 174, the hardware pipelines 172 provideinputs to the software pipelines. One or more pipelines serve each ofthe hydrophones in the hydrophone array. Each software pipeline mayprovide, among other things, downconversion and/or filtering. In variousembodiments, the software pipeline may provide for recovery of a messagefrom a hydrophone input 136. In an embodiment, hydrophone may be servedby pipelines for one or more of interpreting, distinguishing,deconstructing and/or decoding a message such as a multicomponentmessage.

In the receive beamforming or steering block 176, the software pipelines174 provide beamformer inputs. Beamformer functionality includes phaseshifting and/or time delay and summation for multiple input signals. Inan embodiment, a beamformer is provided for each of multiple codedsignals. For example, where software pipelines operate using two codedsignals, inputs to a first beamformer are software pipelines decoding afirst code and inputs to a second beamformer are software pipelinesdecoding a second code.

In the processor block 178, the beamformers of the beamformer block 176provide processor inputs. Processor functionality may include any one ormore of bottom detection, backscatter processing, data reduction,Doppler processing, acoustic imaging, and generation of a short timeseries of backscatter sometimes referred to as “snippets.”

In an embodiment, a management section 192 and a sensor interfacesection 190 are provided. The management section includes an interfacemodule 194 and/or a workstation computer 196. The sensor interfacesection provides for interfacing signals from one or more sensors ES1,ES2, ES3 such as sensors for time (e.g. GPS), motion, attitude, andsound speed.

In various embodiments, control and/or control related signals areexchanged between the management section 192 and one or more of thepower amplifier block 152, software pipelines block 174, transmitbeamformer block 156, receive beamformer block 176, signal generatorblock 158, processor block 178. And, in various embodiments sensorinterface section data 190 are exchanged with the management section 192and the processor block 178.

FIG. 1D shows portions of an exemplary multibeam echo sounder system(“MBES”) 100D. The echo sounder system includes a transducer section120, a transmitter section 150, and a receiver section 170. Someembodiments include an interface section 190 and/or a management section192.

In the embodiment shown, a message 153 incorporating quantity N signals,for example N coded signals, is used to excite plural projectors in aprojector array and a receiver having quantity T hardware or softwarepipelines and (T*N) hardware or software pipelines may be used toprocess T hydrophone signals for recovery of echo information specificto each of the N coded signals.

The transmitter section 150 is for exciting the projector array 130. Thesection includes a signal generator block 158, a transmit beamformerblock 156, a summation block 154, and a power amplifier block 152.

The signal generator block 158 may generate quantity N signals ormessage components, for example N coded signals (e.g., Scd1 . . . ScdN).In some embodiments, each of plural signals within a message shares acommon center frequency and/or a common frequency band. And, in someembodiments, each of plural signals within a message has a unique,non-overlapping frequency band.

A transmit beamformer block 156 receives N signal generator blockoutputs. For each of the N signals generated, the beamformer blockproduces a group of output beam signals such that there N groups ofoutput beam signals.

The summation block 154 receives and sums the signals in the N groups ofoutput beams to provide a summed output 153.

The power amplifier block 152 includes quantity S amplifiers for drivingrespective projectors in the projector array 130. Each power amplifierreceives the summed output or a signal that is a function of the summedoutput 153, amplifies the signal, and drives a respective projector withthe amplified signal.

An array of quantity T hydrophones 140 is for receiving echoes ofacoustic/pressure waves originating from the projector array 130. Theresulting hydrophone signals are processed in the receiver section 170which includes a hardware pipeline block 172, a software pipeline block174, a receive beamformer block 176, and a processor block 178.

In the hardware pipeline block 172, T pipelines provide independentsignal conditioning and analog-to-digital conversion for each of the Thydrophone signals.

In the software pipeline block 174, (T*N) software pipelines may providedownconversion and/or filtering for each of the T hardware pipelineoutputs. Means known in the art, for example filtering such as band passfiltering, may be used to distinguish different signals such as signalsin different frequency bands. As shown, each of T hardware pipelineoutputs 181, 182, 183 provides N software pipeline inputs a,b and c,dand e,f (i.e., 3*2=6 where T=3 and N=2).

In the receive beamformer block 176, (T*N) software pipeline block 174outputs are used to form N groups of beams. A beamformer is provided foreach of N codes. For example, where there are T=3 hydrophones andsoftware pipelines process N=2 codes, inputs to a first beamformer aresoftware pipelines processing the first code a1, c1, e1 and inputs to asecond beamformer are software pipelines processing the second code b1,d1, f1.

In the processor block 178, N processors receive respective groups ofbeams formed by the beamformer block 176. Processor block 178 data areexchanged with a management section 192 and sensor interface 190 dataES1, ES2, ES3 are provided to the management section and/or theprocessor block.

In various embodiments control signals from the management block 192 areused to make power amplifier block 152 settings (e.g., for “S” poweramplifiers for shading), to control transmit 156 and receive 176beamformers, to select software pipeline block 174 operatingfrequencies, and to set signal generator block 158 operatingfrequencies.

As the above illustrates, the disclosed echo sounder transmitter mayconstruct a message incorporating N components such as N coded signals.And, the echo sounder may utilize a receiver having T hardware pipelinesand (T*N) software pipelines to process T hydrophone signals forrecovery of echo information specific to each of the N messagecomponents.

FIGS. 1E-F show portions of an exemplary multibeam echo sounder system(“MBES”) 100E-F. See FIG. 1H for nomenclature 100H. The echo soundersystem includes a transducer section 120, a transmitter section 150, anda receiver section 170. Some embodiments include an interface section190 and/or a management section 192.

In the embodiment shown, a message 153 incorporating first, second, andthird message components such as coded signals Scd1, Scd2, Scd3 whereN=3 is used to excite three projectors in a projector array, and areceiver having three hardware pipelines and nine software pipelines isused to process three hydrophone signals T=3 to recover echo informationspecific to each of the N message components.

The transmitter section 150 is for exciting the projector array 130. Thesection includes a signal generator block 158, a transmit beamformerblock 156, a summation block 154, and a power amplifier block 152.

In the signal generator block 158, signals are constructed, generated,recalled and/or otherwise provided. Here, an exemplary process isdepicted with e.g., N=3 signal generators. In respective beamformers ofthe beamformer block 156, multiple beams are generated from each signal.In a summation block 154, the beams are combined to produce a summationblock output signal or transmit message 153.

The transducer block 120 includes a projector array 130 and a hydrophonearray 140 arranged, for example, as a Mills Cross. As shown, there arethree projectors 131 in the projector array and three hydrophones 141 inthe hydrophone array. In the power amplifier block 152, the summedsignal or transmit message 153 is an input to power amplifiers drivingrespective projectors.

Applicant notes that for convenience of illustration, the projector andhydrophone counts are limited to three. As skilled artisans willappreciate, transducer arrays do not require equal numbers of projectorsand hydrophones nor do the quantities of either of these types oftransducers need to be limited to three. For example, a modern multibeamecho sounder might utilize 1 to 96 or more projectors and 64 to 256 ormore hydrophones.

The array of T=3 hydrophones 141 is for receiving echoes resulting fromthe acoustic/pressure waves originating from the projector array 130.The resulting hydrophone signals are processed in the receiver section170 which includes a hardware pipeline block 172, a software pipelineblock 174, a receive beamformer block 176, and a processor block 178.

In the hardware pipelines block 172, each of T=3 hardware pipelinesprocesses a respective hydrophone 141 signal through analog componentsincluding an analog-to-digital converter. In the embodiment shown, ahardware pipeline provides sequential signal processing through a firstamplifier, an anti-aliasing filter such as a low pass anti-aliasingfilter, a second amplifier, and an analog-to-digital converter.

In the software pipelines block 174, each of the T=3 hardware pipelineoutputs is processed through N=3 software pipelines with downconversionand band pass filtering. In the embodiment shown, a software pipelineprovides sequential signal processing including processing through amixer (an oscillator such as local oscillator may be coupled to themixer), a bandpass filter, and a decimator. Communications may occur viacommunications links between any of the processor block 178, the signalgenerator block 158, the hardware pipelines block 172, the softwarepipelines block 174, the and the beamformer block 176. See for exampleFIGS. 1C-D.

Each software pipeline may have a single mixer and/or each hardwarepipeline may have no mixer. A processor 178 may control gain of a firstand/or a second hardware pipeline amplifier. A processor may provide fortuning, for example via a processor controlled oscillator coupled with amixer.

In the receive beamformer block 176, each of N=3 beamformers processessignals. As such, i) a first set of three software pipeline outputscorresponding to a first coded signal are processed by a firstbeamformer, ii) a second set of three software pipeline outputscorresponding to a second coded signal are processed by a secondbeamformer, and (iii) a third set of three software pipeline outputscorresponding to a third coded signal are processed by a thirdbeamformer. Notably, beamformers may be implemented in hardware orsoftware. For example, one or more beamformers may be implemented in oneor more field programmable gate arrays (“FPGA”).

In the processor block 178, each of N=3 processors are for processingrespective beamformer outputs. Here, a first plurality of beamsgenerated by the first beamformer is processed in a first processor, asecond plurality of beams generated by the second beamformer isprocessed in a second processor, and a third plurality of beamsgenerated by the third beamformer is processed in a third processor.

Processor outputs interconnect with a management section 192. Notably,one or more processors may be implemented in a single device such as asingle processor or digital signal processor (“DSP”) or in multipledevices such as multiple signal processors or digital signal processors.

Complementary data may be provided via, inter alia, a sensor interfacesection 190 that is interfaced with a plurality of sensors ES1, ES2,ES3. The sensor interface module may provide sensor data to themanagement section 192 and/or to processors in the processor block 178.

The management section 192 includes a sonar interface 194 and/or aworkstation computer 196. In various embodiments control signals fromthe management block 192 are used for one or more of making poweramplifier block 152 settings (e.g., for array shading), controllingtransmit beamformers 156 and receive beamformers 176, selecting softwarepipeline block 174 operating frequencies, setting set signal generatorblock 158 operating frequencies, and providing processor block 178operating instructions.

Applicant notes that the echo sounder systems of FIGS. 1C-F may be usedto process hydrophone returns from targets i) present within anensonified volume of the water body, ii) upon an ensonified surface ofthe bottom, or lying within an ensonified volume of the bottom.

In various embodiments, the MBES of FIGS. 1E-F distinguishes amongsignals based on frequency or frequency band. In various embodiments,the MBES of FIGS. 1E-F does not distinguish among signals using matchedfiltering.

Referring again to FIG. 1E.

FIG. 1E and FIG. 1G show portions of an exemplary multibeam echo soundersystem (“MBES”) 100E-F. See FIG. 1H for nomenclature. The echo soundersystem includes a transducer section 120, a transmitter section 150, anda receiver section 170. Some embodiments include an interface section190 and/or a management section 192.

In the embodiment shown, a message 153 incorporating first, second, andthird message components such as coded signals Scd1, Scd2, Scd3 whereN=3 is used to excite three projectors in a projector array, and areceiver having three hardware pipelines and nine software pipelines isused to process three hydrophone signals T=3 to recover echo informationspecific to each of the N message components.

The transmitter section 150 is for exciting the projector array 130. Thesection includes a signal generator block 158, a transmit beamformerblock 156, a summation block 154, and a power amplifier block 152.

In the signal generator block 158, signals are constructed, generated,recalled and/or otherwise provided. Here, an exemplary process isdepicted with e.g., N=3 signal generators. In respective beamformers ofthe beamformer block 156, multiple beams are generated from each signal.In a summation block 154, the beams are combined to produce a summationblock output signal or transmit message 153.

The transducer block 120 includes a projector array 130 and a hydrophonearray 140 arranged, for example, as a Mills Cross. As shown, there arethree projectors 131 in the projector array and three hydrophones 141 inthe hydrophone array. In the power amplifier block 152, the summedsignal or transmit message 153 is an input to power amplifiers drivingrespective projectors.

Applicant notes that for convenience of illustration, the projector andhydrophone counts are limited to three. As skilled artisans willappreciate, transducer arrays do not require equal numbers of projectorsand hydrophones nor do the quantities of either of these types oftransducers need to be limited to three. For example, a modern multibeamecho sounder might utilize 1 to 96 or more projectors and 64 to 256 ormore hydrophones.

The array of T=3 hydrophones 141 is for receiving echoes resulting fromthe acoustic/pressure waves originating from the projector array 130.The resulting hydrophone signals are processed in the receiver section170 which includes a hardware pipeline block 172, a software pipelineblock 174, a receive beamformer block 176, and a processor block 178.

In the hardware pipelines block 172, each of T=3 hardware pipelinesprocesses a respective hydrophone 141 signal through analog componentsincluding an analog-to-digital converter. In the embodiment shown, ahardware pipeline provides sequential signal processing through a firstamplifier, an anti-aliasing filter such as a low pass anti-aliasingfilter, a second amplifier, and an analog-to-digital converter.

In the software pipelines block 174, each of the T=3 hardware pipelineoutputs is processed through N=3 software pipelines with downconversionand matched filtering. In the embodiment shown, a software pipelineprovides sequential signal processing through a mixer (an oscillatorsuch as local oscillator may be coupled to the mixer), a bandpassfilter, a decimator, and a matched filter. Communications may occur viacommunications links between any of the processor block 178, the signalgenerator block 158, the hardware pipelines block 172, the softwarepipelines block 174, the and the beamformer block 176. See for exampleFIGS. 1C-D.

Each software pipeline may have a single mixer and/or each hardwarepipeline may have no mixer. A processor 178 may control gain of a firstand/or a second hardware pipeline amplifier. A processor may provide fortuning, for example via a processor controlled oscillator coupled with amixer.

In the receive beamformer block 176, each of N=3 beamformers processessignals. As such, i) a first set of three software pipeline outputscorresponding to a first coded signal are processed by a firstbeamformer, ii) a second set of three software pipeline outputscorresponding to a second coded signal are processed by a secondbeamformer, and (iii) a third set of three software pipeline outputscorresponding to a third coded signal are processed by a thirdbeamformer. Notably, beamformers may be implemented in hardware orsoftware. For example, one or more beamformers may be implemented in oneor more field programmable gate arrays (“FPGA”).

In the processor block 178, each of N=3 processors are for processingrespective beamformer outputs. Here, a first plurality of beamsgenerated by the first beamformer is processed in a first processor, asecond plurality of beams generated by the second beamformer isprocessed in a second beamformer, and a third plurality of beamsgenerated by the third beamformer is processed in a third beamformer.

Processor outputs interconnect with a management section 192. Notably,one or more processors may be implemented in a single device such as asingle processor or digital signal processor (“DSP”) or in multipledevices such as multiple signal processors or digital signal processors.

Complementary data may be provided via, inter alia, a sensor interfacesection 190 that is interfaced with a plurality of sensors ES1, ES2,ES3. The sensor interface module may provide sensor data to themanagement section 192 and/or to processors in the processor block 178.

The management section 192 includes a sonar interface 194 and/or aworkstation computer 196. In various embodiments control signals fromthe management block 192 are used for one or more of making poweramplifier block 152 settings (e.g., for array shading), controllingtransmit 156 and receive 176 beamformers, selecting software pipelineblock 174 operating frequencies, setting set signal generator block 158operating frequencies, and providing processor block 178 operatinginstructions.

FIG. 2 shows a message cycle 200. The cycle includes a sequence ofoperations with transmission of a message during a time t1 and receptionof a message during a time t3. Transmission of a message refers to theprocess that excites the projector array 130 and reception of a messagerefers to the complementary process that interprets the message echoreceived by the hydrophone array 140. A wait time t2 that variesprimarily with range, angle, and sound speed may be interposed betweenthe end of the message transmission and the beginning of the messagereception. This wait time may be determined by round trip travel timefor the longest sounding range, for example a return from the mostdistant cell in a swath ensonified by the projector array. In someembodiments, the transmit message length is in a range of 10 to 60microseconds. In some embodiments, the transmit message length is about10 milliseconds.

Sonar Data Compression

We turn now to embodiments that illustrate sonar data compression. Theseembodiments include ensonification of a fan with an appropriate messageand selecting the strongest returns for viewing and use.

FIG. 3A shows a message 300A with a frequency centered signal sentbetween t_(a) and t_(b). The message may be a signal of many types:continuous wave (CW), frequency modulated (FM), orthogonal spreadspectrum (OSS), phase-coded (PC), pulse train (PT), or low probabilityof intercept (LPI). In response to the message sent, data are returnedand beamformed

Each of the beamformed data points returned is represented by both amagnitude and a phase, and each beam is associated with a differentsteering angle, or beam angle, relative to the array face. Notably, thereceive window duration (t) may be equal to or greater than theround-trip travel time of an echo of the farthest expected return, forexample the farthest expected return reflected from the sea floor.

FIG. 3B shows a perspective view 300B of the beams formed by thehydrophone array 140 when receiving echoes. To illustrate themethodology a multibeam echo sounder utilizing 16 beams, with 16different beam angles, is chosen. Notably, the beams may reflect fromthe sea floor or be gated with range bins for water column assessment.

FIG. 3C shows a view of the beams 300C formed by the hydrophone arraywhen viewed from the front of the boat and along the longitudinal axisof the boat. As seen, eight beams to either side of nadir are formed anddata may be collected in accordance with number of

Data Points=Q*t*fs

where Q is the number of beams, t is the receive window duration inseconds, fs is the receiver sampling rate in Hz, and each data point isrepresented by two values: a magnitude and phase. Note that the numberof samples collected ‘s’ from each beam is (t*fs).

FIG. 3D shows a matrix of the data points 300D collected during the timespan “t”. Each entry B_(x,y) in the matrix is a complex quantityproviding a magnitude and phase for the x^(th) sample and the y^(th)beam. As shown, there are “s” samples collected in time span “t”. (Note:Samples and data points may be different. For example samples aretime/range tics set according to the sample rate of the receiver. Forexample data points are the output of the beamformers at a givensample.)

In the compression method, the magnitudes of beam data for all beams ata given sample (row of matrix 300D) are compared, and the beam angles αand magnitudes (|B|) associated with N greatest magnitudes are selectedto populate a matrix ß for that sample. This matrix ß, with columns ofbeam angles and magnitudes, or data derived therefrom may be presentedto the user as a compressed presentation or view of the data with acompression ratio of N:Q.

Note that when finding the beam with the greatest magnitude for a givensample, one can simply sort on magnitude. Other techniques includefinding the peak of a moving averaging window and calculating an energycenter of mass.

FIG. 3E shows a matrix of the data points 300E collected during the timespan “t”. As before, each entry B_(x,y) in the matrix is a complexquantity providing a magnitude and phase for the x^(th) sample and they^(th) beam. And, as shown there are “s” samples collected in time span“t”.

However, here beams with the largest two magnitudes are selected (N=2)for each sample (row of the matrix 300E) such that a matrix ßß resultswith 2N columns and s rows. This matrix ßß or data derived therefrom maybe presented to the user as a compressed presentation or view of thedata with a compression ratio of N:Q.

How many magnitudes are selected from each row of the matrix depends onthe user. It is normally the case that the number N selected is muchless than the number of beams Q.

In FIG. 3C, all of the available beams are used. In other embodiments,less than all of the available beams may be used.

Subsectors in Sonar Data Compression

FIG. 4A shows a compressed view that is focused on a subsector. Thesubsector encompasses beams 7 through 13. In this example, one beamangle (N=1) will be reported for each sample. In this example, only datafrom beams 7 through 13 will be considered when finding the maximummagnitude as beams 7 and 13 are the limits of the defined subsector.

As shown in FIG. 4B, beam data with magnitudes and phases are indicatedby vectors B_(1,7) . . . B_(s,13). Note that no beam indices extendbeyond the limits at beams 7 and 13. Further, a matrix ß indicates foreach sample the beam angle α that has the largest magnitude |B|. Asmentioned earlier, N may be set to a value greater than 1 such thelargest magnitude and also progressively smaller magnitudes are selectedfor each sample.

This type of compression may be useful where there is a feature presentin other beams that is to be avoided. This type of compression may beuseful where there is a feature present in beams 7 through 13 upon whichto focus.

In FIG. 3C, all of the available beams are in a single sector. In otherembodiments, the beams may be divided among multiple sectors, forexample two sectors. The number of subsectors into which the wholesector is divided is represented by S.

FIG. 4C shows a compressed view that is divided into two sub-sectors.Data from the first subsector shown in FIG. 4D encompass port beams 1-8and data from the second subsector shown in FIG. 4E encompass starboardbeams 9-16. In this example S*N beam angles and magnitudes, where S=2and N=1, will be reported for each sample for a data compression ratioS*N:Q.

In FIG. 4D, there is a matrix of values ßp which represents the largestmagnitude return at each sample value when only the port beams areconsidered. In FIG. 4E, there is a matrix of values ßr which representsthe largest magnitude return at each sample value when only thestarboard beams are considered. As mentioned earlier, N may be set to avalue greater than 1 such the largest magnitude and also progressivelysmaller magnitudes are selected for each sample.

This type of compression may be useful where the returns from one side(eg. p) are much stronger than the returns from the other side (eg. r)insofar as the subsectors assure a view that has content from bothsides.

In FIG. 3C, all of the available beams are in a single sector. In otherembodiments, the beams may be divided among multiple sectors, forexample three sectors.

FIG. 4F shows a compressed view that is divided into three sub-sectors(S=3). As shown in FIG. 4G, the first subsector includes data from twobeams, 8 and 9. As shown in FIG. 4H, the second subsector includes beamsthat are to port of the nadir beam, beams 1-7. As shown in FIG. 4I, thethird subsector includes beams that are to starboard of the nadir beam,beams 10-16. In this example there are S*N beam angles where S=3 and N=1will be reported for each sample for a data compression ratio S*N:Q.

In FIG. 4G, there is a matrix ßc of values α and |B| which representsthe beam angle and magnitude of the largest magnitude return at eachsample value when the central beams are considered. In FIG. 4H, there isa matrix ßp of values α and |B| which represents the largest magnitudereturn at each sample value when the port beams are considered. In FIG.4I, there is a matrix ßr of values α and |B| which represents thelargest magnitude return at each sample value when the starboard beamsare considered. As mentioned earlier, N may be set to a value greaterthan 1 such the largest magnitude and also progressively smallermagnitudes are selected for each sample.

This type of compression may be useful where there is a central featureto be followed and there is a need to provide a context for the centralfeature. For example, the central feature might be a pipeline followedby the central beams and the context might be the zones to either sideof the pipeline followed by the port and starboard beams.

As mentioned above, returns may be range gated. The returns may be rangegated to focus on the sea floor or the returns may be range gated tofocus on some portion of the water column.

Water Column Sonar Data Compression

FIG. 5A shows a nadir beam emanating from the face of a transducer array500A. If the beam is range gated at a maximum and minimum altitude, onlythose samples representing reflections that occurred within the altitudelimits will be considered for data compression. Using the techniquesdescribed above, the strongest reflections from only a portion of thewater column are reported when range gates are applied.

FIG. 5B shows a nadir beam and an outer beam emanating from an arrayface 500B. In this example the range gates are set to capture the seafloor with a minimum altitude above the expected floor elevation and amaximum altitude below the expected floor elevation.

In an exemplary scan of the sea floor, the nadir beam is range gatedbetween sample 5000 and 8000. In similar fashion, the outer beam isgated in the range gated between sample 9000 and 15000. That is to saythat the reflections of interest occur in the range of samples 5000 to8000 in the nadir beam and somewhat later in time, between samples 9000and 15000, in the outer beam.

FIG. 5C shows a nadir beam and an outer beam emanating from an arrayface 500C. In this example the range gates are set to capture a portionof the water column with a maximum altitude above the sea floorelevation and a minimum altitude above the sea floor elevation.

In an exemplary scan of the sea floor, the nadir beam is range gatedbetween sample 1000 and 7000. In similar fashion, the outer beam isgated in the range gated between sample 2000 and 13000. That is to saythat the reflections of interest occur in the range of samples 1000 to7000 in the nadir beam and somewhat later in time, between samples 2000and 13000, in the outer beam.

The techniques described above can be applied jointly, allowing for agating in altitude within multiple sub-sectors. In various cases, thereporting of magnitude and beam angle associated with peak beam indicesresults in a significant data compression.

Beam Angle Precision

As described above, the reported beam angles are the nominal beam anglesassigned to each beam by the beamformer. As such, these beam angles maybe viewed as crude estimates of actual angle.

Angle measurement to the points of backscatter resulting in the N peakmagnitudes may be improved. For example, a split array phase differencetechnique may be used to better estimate these angles. See e.g. Denbigh,P. (1989), “Swath Bathymetry: Principles of operation and an Analysis ofErrors,” IEEE J. of Oceanic Eng. 14(4), 289-298.

The technique begins by practically dividing the receive array in halfand treating it as two subarrays with half the total elements each. Abeamformer is applied to the elements of each half, steering a beam inthe direction of the N beam angles α identified earlier for each of thes samples.

This will result in two complex numbers representing each half of thearray for each sample index and beam angle. The phase difference betweeneach pair of complex values is measured as ΔΦ and is used to calculatethe angle Φ of the echo arrival relative to the array axis via the knownrelationship:

ΔΦ=2π*a/λ*sin(Φ)

where λ is the acoustic wavelength at the given center frequency fc andspeed of sound at the sonar c, and a is the distance between the phasecenters of the two sub arrays.

The fine angle measurement is repeated N times for all s samples. And,in a final report, N*s peak magnitudes and corresponding angles arereturned to the user.

Because the sample rate “fs” is known, each sample index “nn” can beconverted into a travel time “tt” and a range “r”. The relationshipsare:

tt=nn/fs

and

r=tt*c/w

The sonar data compression methods mentioned above provide water columnand bathymetry swath data with high angular and range resolution usingonly a fraction of the data required by conventional imaging. Inaddition to data compression benefits, the algorithm inherently filtersout relatively weak returns from inconsequential targets that mightotherwise be distracting to an operator if visualized.

It also eliminates undesirable false returns often seen in all non-nadirbeams at the range bin of the nadir beam altitude caused when the strongnadir return is amplified by a sidelobe of a non-nadir beam. Becausethese false returns all share the same range/time sample, the maximumover all beams at that sample will naturally be at the nadir beam; thealgorithm will select the true maximum at nadir and ignore all others.

In all cases above, the backscatter response results from ensonificationat a single center frequency fc. This response can be enhanced.

Multispectral Sonar Data Compression

Reflectors and scattering centers of different sizes and roughnesses mayhave varying echo responses dependent upon the center frequency of thesound which impinges on them. This characteristic may be exploited inbottom classification missions using multispectral ensonification. Forexample, where a sea floor is ensonified with multiple frequencies andthe echoes are compared in order to segment and/or classify the bottomsurface.

This characteristic may also be exploited where the water column isconcerned. For example, where scatterers in the water column areensonified with multiple frequencies and the echoes are compared inorder to classify material in the water column.

The sonar data compression methods above may be enhanced where signalswith multiple center frequencies, for example multiple widely spacedcenter frequencies, are used to ensonify reflectors and scatteringcenters. Per the description of the MBES above, each of n differentsignals will have its own software pipeline and beamformer. Thecompression algorithm is then applied to each of the n beamformeroutputs individually, resulting inn pairs of beam angle α and magnitude|B| values saved for each of s samples.

During multifrequency operations, it can be advantageous to comparereturns at different frequencies received at the same time from the samescatterers. However, the peak magnitude may not be at the same beam andsame sample for all n center frequencies, so the compression algorithmas described above may not capture simultaneous frequency dependentinformation from the same scatterers at each sample. Therefore, inanother embodiment, when the algorithm identifies the beam angle withthe peak magnitude for a given sample and center frequency, it will alsorecord the magnitude of beam data at the same beam angle and sample forall other (n−1) center frequencies/signals.

FIG. 6A shows multimission message content and message constructiontable for exemplary multimission surveys 600A. As seen in the table, amultimission survey is carried out using a multimission message whichmay be constructed in a particular manner.

A first multimission survey includes a first bathymetry mission and asecond bathymetry mission. Typically, intermediate bands are not used.

The first bathymetry mission utilizes a relatively low frequency bandwith a CW or FM signal. The second bathymetry mission utilizes arelatively high frequency band with a CW or FM signal. These signals maybe serialized or paralleled in a single ping message. These signals maybe sent in respective pings as a multi-ping message. Having readapplicant's disclosure, skilled artisans will recognize the advantagesof this multimission survey which, among other things, resolves longstanding problems associated with choosing one or the other of a highfrequency (relatively high resolution/relatively short range) survey ora low frequency (low resolution/long range) survey. In an embodiment,the frequency bands are widely spaced with band gaps therebetween.

A second multimission survey includes a first waterbody bottom orseafloor characterization mission and a second waterbody bottom orseafloor characterization mission. Typically, intermediate bands may beused.

The first waterbody bottom mission utilizes a relatively low frequencyband with a CW signal. The second waterbody bottom mission utilizes arelatively high frequency band with a CW signal. These signals may beparalleled in a single ping message. These signals may be sent inrespective pings in a multi-ping message. Having read applicant'sdisclosure, skilled artisans will recognize the advantages of thismultimission survey which, among other things, resolves long standingproblems associated with obtaining survey data sufficient for use insegmenting and/or classifying a waterbody bottom surface and/orwaterbody bottom subsurface where the echo response varies with sonarfrequency. Notably beneficial to bottom segmentation and/or bottomclassification survey missions are parallel signals in a single pingmessage that provide for echoes at multiple frequencies from the samebackscatterers.

A third multimission survey includes a first waterbody bottomcharacterization or segmentation mission and a second bathymetrymission. Typically, intermediate bands may be used.

The first waterbody bottom characterization or segmentation missionutilizes a relatively lower frequency band with a CW signal or, in someembodiments, two or three CW signals. The second bathymetric missionutilizes a relatively higher frequency band with an FM signal. Thesesignals may be serialized or paralleled in a single ping. These signalsmay be sent in respective pings in a multi-ping message. Having readapplicant's disclosure, skilled artisans will recognize the advantagesof this multimission survey which, among other things, resolves longstanding problems associated obtaining survey data useful for bothcharacterization or segmentation of the waterbody bottom and bathymetryin a single pass.

A fourth multimission survey includes a first Doppler navigation missionand a second multi-fan bathymetric mission. Typically, no intermediatebands are used. Multi-fan may refer to plural quasi-parallel fans orswaths including a first fan and one or more additional fans steeredfore and/or aft of the first fan. For example, a multi-fan mission mightuse a central athwartship fan and quasi-parallel fans to either side ofthe athwartship fan.

The first Doppler navigation mission utilizes a relatively lowerfrequency band with a phase coded signal such as a Barker code. Thesecond multi-fan bathymetric mission utilizes a relatively highfrequency band with a spread spectrum signal such as orthogonal codedpulses (OCP). These signals may be serialized in a single ping. BecauseOCP signals are distinguished by their code pattern, multiple ones ofthese coded signals may be used to ensonify respective parallel orsomewhat parallel swaths in a fan-like arrangement. The returns from theOCP signals are distinguished using the code patterns. These signals maybe serialized in a single ping or sent in respective pings in amulti-ping message. Having read applicant's disclosure, skilled artisanswill recognize the advantages of this multimission survey which, amongother things, resolves long standing problems associated with alongtrack sounding density, multi-aspect multibeam surveys, and concurrentbathymetric and navigation operations.

A fifth multimission survey includes a first sub-bottom profilingmission and a second bathymetry mission. Typically, intermediate bandsmay be used.

The first waterbody bottom mission utilizes a relatively low frequencyband with a CW signal. The second waterbody bottom mission utilizes arelatively high frequency band with a CW signal. These signals may beparalleled in a single ping message. These signals may be sent inrespective pings in a multi-ping message. Having read applicant'sdisclosure, skilled artisans will recognize the advantages of thismultimission survey which, among other things, resolves long standingproblems associated with obtaining survey data sufficient for use insub-bottom profiling and bathymetry. Notably beneficial to sub-bottomprofiling is parallel transmission of both the sub-bottom profilingsignal(s) and the bathymetry signal(s) such that the signals arereturned from the same backscatterers.

A sixth multimission survey includes a first water columncharacterization mission and a second water column characterizationmission. Typically, intermediate bands may be used.

The first water column mission utilizes a relatively low frequency bandwith a CW or FM signal. The second water column mission utilizes arelatively high frequency band with a CW or FM signal. These signals maybe serialized or paralleled in a single ping message. These signals maybe sent in respective pings in a multi-ping message. Having readapplicant's disclosure, skilled artisans will recognize the advantagesof this multimission survey which, among other things, resolves longstanding problems associated with obtaining water column data sufficientfor use in segmenting and/or classifying water column scatterers wherethe echo response varies with sonar frequency. Notably beneficial towater column segmentation and/or water column classification missionsare parallel signals in a single ping message that provide for echoes atmultiple frequencies from the same backscatterers.

A seventh multimission survey includes a first water columncharacterization or segmentation mission and a second bathymetrymission. Typically, intermediate bands may be used.

The first water column characterization or segmentation mission utilizesa relatively lower frequency band with a CW or FM signal or, in someembodiments, two or three CW or FM signals. The second bathymetricmission utilizes a relatively higher frequency band with an FM signal.These signals may be serialized or paralleled in a single ping. Thesesignals may be sent in respective pings in a multi-ping message. Havingread applicant's disclosure, skilled artisans will recognize theadvantages of this multimission survey which, among other things,resolves long standing problems associated obtaining survey data usefulfor both characterization or segmentation of the water column andbathymetry in a single pass.

FIGS. 6B-H show exemplary messages with particular signal frequenciesfor use in multimission surveys 600B-H.

FIG. 6B shows a first multimission survey including a first long rangebathymetry mission and a second high resolution bathymetry mission 600B.

The first long range bathymetry mission utilizes a relatively lowerfrequency band with a CW or FM signal having a center frequency of about200 kHz and respective bandwidths of about 5 to 30 kHz and about 30 to60 kHz.

The second high resolution bathymetry mission utilizes a relativelyhigher frequency band with a CW or FM signal having a center frequencyof about 700 kHz and respective bandwidths of about 20 to 60 kHz andabout 20 to 60 kHz. These signals may be paralleled (as shown) in asingle ping message. These signals may be sent in respective pings in amulti-ping message.

FIG. 6C shows a second multimission survey including three bottomcharacterization or segmentation missions 600C.

The first bottom characterization or segmentation mission utilizes arelatively low frequency band with a CW signal having a center frequencyof about 50 kHz and a bandwidth of about 2 to 10 kHz.

The second bottom characterization or segmentation mission utilizes anintermediate frequency band with a CW signal having a center frequencyof about 100 kHz and a bandwidth of about 2 to 10 kHz.

The third bottom characterization or segmentation mission utilizes arelatively higher frequency band with a CW signal having a centerfrequency of about 150 kHz and a bandwidth of about 2 to 10 kHz. Thesesignals may be paralleled (as shown) in a single ping message. Thesesignals may be sent in respective pings in a multi-ping message.

These center frequencies at 50, 100, 150 kHz may be shifted to avoidharmonics. For example, where the 50 kHz center frequency locates thecenter of a first frequency band, first harmonics may be avoided byshifting the 50 kHz center frequency by a frequency incrementapproximating the width of the first frequency band. For example, wherethe 150 kHz center frequency locates the center of a second frequencyband, second harmonics may be avoided by shifting the 150 kHz centerfrequency by a frequency increment approximating the width of the secondfrequency band. As skilled artisans will understand, yet other similarchanges to the above center frequencies may avoid harmonics.

FIG. 6D shows a third multimission survey including a first bottomcharacterization or segmentation mission and a second bathymetry mission600D.

The first bottom characterization or segmentation mission utilizes arelatively low frequency band with three CW signals having respectivecenter frequencies of about 50, 150, 250 kHz. As described above, thesecenter frequencies may be shifted to avoid harmonics. And where, ashere, plural signals in respective bands are used to fulfill a singlemission, the mission may be referred to as a multiband mission.

The second bathymetric mission utilizes a relatively higher frequencyband with an FM signal having a center frequency of about 400 kHz and abandwidth of about 30 to 60 kHz. These signals may be serialized orparalleled (as shown) in a single ping message. These signals may besent in respective pings in a multi-ping message. Notably, the phrase“about . . . kHz” refers to manufacturing and operating tolerancesassociated with generation, transmission, reception, and/ordeconstruction of signals by modern day sonar equipment used forbathymetry and/or bottom segmentation.

FIG. 6E shows a fourth multimission survey including a first navigationmission and a second bathymetry mission 600E.

The first navigation mission utilizes a relatively lower frequency bandwith a phase coded signal having a center frequency of about 100 kHz anda bandwidth of about 60 kHz.

The second bathymetry mission utilizes a relatively higher frequencyband with three OSS signals having a center frequency of 400 kHz. TheOSS signals may have similar bandwidths and occupy a common band havinga bandwidth of about 100 kHz. Where, as here, there are multiple OSSsignals occupying a common band, this may be referred to as amultisignal band and the signals within this band may be referred to asa package of signals.

These signals may be sent in a message having a combination parallel andserial format with the bathymetry mission signals sent in parallel andthe navigation signal sent before or after the bathymetry signals.

FIG. 6F shows a fifth multimission survey including a first sub-bottomprofiling mission and a second bathymetry mission 600F.

The first sub-bottom profiling mission utilizes a relatively lowfrequency band with a CW signal having a center frequency of in a rangeof about 10 to 30 kHz, here 15 kHz, and a bandwidth of about 1 kHz.

The second bathymetry mission utilizes a relatively high frequency bandwith a CW signal having a center frequency of about 200 kHz and abandwidth of about 20 to 60 kHz. These signals may be paralleled (asshown) in a single ping message. These signals may be sent in respectivepings in a multi-ping message.

FIG. 6G shows a sixth multimission survey including a first water columnmission and a second water column mission 600G.

The first water column mission utilizes a relatively low frequency bandwith a CW or FM signal having a center frequency of about 100 kHz andrespective bandwidths of about 10 to 20 kHz and about 10 to 30 kHz.

The second water column mission utilizes a relatively higher frequencyband with a CW or FM signal having a center frequency of about 150 kHzand respective bandwidths of about 10 to 20 kHz and about 10 to 30 kHz.These signals may be paralleled (as shown) in a single ping message.These signals may be sent in respective pings in a multi-ping message.

FIG. 6H shows a seventh multimission survey including a first watercolumn mission and a second bathymetry mission 600H.

The first water column mission utilizes a relatively low frequency bandwith a CW or FM signal having a center frequency of about 100 kHz andrespective bandwidths of about 10 to 30 kHz and about 30 to 60 kHz.

The second bathymetry mission utilizes a relatively higher frequencyband with a CW or FM signal having a center frequency of about 400 kHzand respective bandwidths of about 20 to 60 kHz and about 30 to 60 kHz.These signals may be paralleled (as shown) in a single ping message.These signals may be sent in respective pings in a multi-ping message.Applicant notes the center frequencies of the signals mentioned inconnection with FIGS. 6A-E are examples. In various embodiments, thesecenter frequencies may vary in ranges of +/−5%, +/−10%, +/−25% and/or+/−50%. Applicant notes that the bandwidths of the signals mentioned inconnection with FIGS. 6A-E are examples. In various embodiments, thesebandwidths may vary in the ranges of +/−5%, +/−10%, +/−25% and/or+/−50%.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to those skilledin the art that various changes in the form and details can be madewithout departing from the spirit and scope of the invention. As such,the breadth and scope of the present invention should not be limited bythe above-described exemplary embodiments, but should be defined only inaccordance with the following claims and equivalents thereof.

What is claimed is:
 1. A method of compressing data from a sonar systemcomprising the steps of: providing an acoustic transceiver with pluraltransducers in a single projector array and plural transducers in asingle hydrophone array; exciting the projector array with a transmittermessage such that a particular geometric space is ensonified; the pluralhydrophones receiving echoes from the geometric space at each of pluraltimes t₁, t₂, . . . ; at one or more the times t_(x), forming Q receivebeams with respective angles of arrival, the Q receive beams formed bythe hydrophone array; associating each of the Q beams with a magnitudeM_(t) _(x) _(,i) indexed by the time t_(x) and beam number i;identifying as characterizing beams one or more beams with largest andnext largest magnitudes at each of the times t_(x); and, using dataassociated with the characterizing beams as a compressedcharacterization of the ensonified space.
 2. The method of claim 1wherein the projector array and the hydrophone array are installed on awater-going vehicle.
 3. The method of claim 1 wherein for each timet_(x) a beam with a first largest magnitude (M_(t) _(x) _(,i))_(max1) isidentified as the characterizing beam such that the data associated withthese characterizing beams is the compressed characterization of theensonified space.
 4. The method of claim 1 wherein for each time t_(x)the beams with first largest magnitude (M_(t) _(x) _(,i))_(max1) andsecond largest magnitude (M_(t) _(x) _(,i))_(max2) are identified as thecharacterizing beams such that the data associated with thesecharacterizing beams is the compressed characterization of theensonified space.
 5. A method of compressing data from a sonar systemcomprising the steps of: providing an acoustic transceiver with pluraltransducers in a single projector array and plural transducers in asingle hydrophone array; exciting the projector array with a transmittermessage such that a particular geometric space is ensonified; the pluralhydrophones receiving echoes from the geometric space at each of pluraltimes t₁, t₂, . . . ; at one or more the times t_(x), forming Q receivebeams with respective angles of arrival, the Q receive beams formed bythe hydrophone array; forming a first subsector from a subset S₁ of u<Qbeams; and, associating each of the u beams with a magnitude M_(t) _(x)_(,i) indexed by the time t_(x) and beam number i; wherein for each timet_(x), the beams with the first, second . . . N<u largest magnitudesamong the u beams (M_(t) _(x) _(,i))_(umax1, umax2 . . . umaxN) arefound and data associated with these characterizing beams are used as acompressed characterization of the ensonified space.
 6. The method ofclaim 5 further comprising: forming T subsectors from respective subsetsS₁, S₂ . . . S_(T) of the Q beams wherein for each time t_(x) and foreach of the T subsectors the subsector beams with the N largestmagnitudes [(M_(t) _(x) _(,i))_(Tmax1, Tmax2 . . . TmaxN]Sx) areidentified as characterizing beams and data associated with thesecharacterizing beams are used as a compressed characterization of anensonified space.
 7. The method of claim 5 wherein the quantity Q mayvary at each time t_(x).
 8. The method of claim 5 wherein echo samplesat each time t_(x) are range gated within minimum and maximum altitudesto generate gated echo samples.
 9. The method of claim 5 wherein thesingle projector array is linear and the single hydrophone array islinear; and, configuring the projector array orthogonally with respectto the hydrophone array to form a Mills cross such that a projectorarray transmit beam and multiple hydrophone array receive beamsintersect.
 10. The method of claim 5 wherein the acoustic transceiversynthesizes n projector signals; for each of the n projector signals,the Q beams are generated with a respective beamformer at each timet_(x-); for each of the times t_(x) identifying as a characterizing beama beam with the largest magnitude (M_(t) _(x) _(,i))_(maxn1) from amongeach of the n beamformers' Q beams; and, using data associated with thecharacterizing beams as a compressed characterization of the ensonifiedspace.
 11. A method of compressing data from a sonar system comprisingthe steps of: providing an acoustic transmitter and an acousticreceiver, plural transducers in a single projector array used by theacoustic transmitter and plural transducers in a single hydrophone arrayused by the acoustic receiver; ensonifying a particular geometric spacewith an acoustic transmitter message emitted from the projector array;at plural times t₁, t₂ . . . receiving echoes from the geometric spacevia the hydrophone array; at one or more of the times t_(x), forming agroup of Q receive beams with respective angles of arrival; recognizingthat at each of the times t_(x) the Q receive beams of each group have amagnitude M_(t) _(x) _(,i) where i denotes the i^(th) receive beam; foreach group of Q receive beams, identifying as a characterizing beam theone or more beams with a largest or next largest magnitudes at each ofthe times t_(x); and, using the recognized magnitudes as a compressedcharacterization of the ensonified space.
 12. The method of claim 11wherein the projector array and the hydrophone array are installed on awater-going vehicle.
 13. The method of claim 11 wherein for each timet_(x) the beam with the first largest magnitude (M_(t) _(x)_(,i))_(max1) is identified as a characterizing beam and data associatedwith these characterizing beams are used as a compressedcharacterization of the ensonified space.
 14. The method of claim 11wherein for each time t_(x) the beams with the first, second . . . N<Qlargest magnitudes (M_(t) _(x) _(,i))_(max1, max2 . . . maxN) areidentified as characterizing beams and data associated with thesecharacterizing beams are used as a compressed characterization of theensonified space.
 15. A method of compressing data from a sonar systemcomprising the steps of: providing an acoustic transmitter and anacoustic receiver, plural transducers in a single projector array usedin the acoustic transmitter and plural transducers in a singlehydrophone array used in the acoustic receiver; ensonifying a particulargeometric space with an acoustic transmitter message emitted from theprojector array; at plural times t₁, t₂ . . . receiving echoes from thegeometric space via the hydrophone array; at one or more of the timest_(x), forming a group of Q receive beams with respective angles ofarrival; recognizing that at each of the times t_(x) the Q receive beamsof each group have a magnitude M_(t) _(x) _(,i) where i denotes thei^(th) receive beam; for each group of Q receive beams, identifying as acharacterizing beam the one or more beams with a largest or next largestmagnitudes at each of the times t_(x); and, using the recognizedmagnitudes as a compressed characterization of the ensonified space. 16.The method of claim 15 further comprising: forming T subsectors fromrespective subsets S₁, S₂ . . . S_(T) of the Q beams wherein for eachtime t_(x) and for each of the T subsectors the subsector beams with theN largest magnitudes [(M_(t) _(x) _(,i))_(Tmax1, Tmax2 . . . TmaxN]Sx)are identified as characterizing beams and data associated with thesecharacterizing beams are used as a compressed characterization of anensonified space.
 17. The method of claim 15 wherein the quantity Q mayvary at each time t_(x).
 18. The method of claim 15 wherein echo samplesat each time t_(x) are range gated within minimum and maximum altitudesto generate gated echo samples.
 19. The method of claim 15 wherein thesingle projector array is linear and the single hydrophone array islinear; and, configuring the projector array orthogonally with respectto the hydrophone array to form a Mills cross such that a projectorarray transmit beam and multiple hydrophone array receive beamsintersect.
 20. The method of claim 15 wherein the acoustic transceiversynthesizes n projector signals; for each of the n projector signals,the Q beams are generated with a respective beamformer at each timet_(x); for each of the times t_(x) identifying as characterizing beamsone or more beams with the largest or next largest magnitudes (M_(t)_(x) _(,i))_(maxn1) . . . (M_(t) _(x) _(,i))_(maxnN) from among thebeamformers output; and using data associated with the characterizingbeams as a compressed characterization of the ensonified space.